1. Field of the Invention
The present invention relates to a method and apparatus for extruding polymer alloys including a first and second polymer material.
More particularly, the present invention relates to a method and apparatus for extruding polymer alloys including a first polymer material and second polymer material, where the method includes the step of extruding the materials in a specially designed extrusion die apparatus.
2. Description of the Related Art
The relevant method described and claimed in the above-mentioned co-pending International Patent Application comprises the steps of a method of forming a film or sheet of thermoplastic polymer alloy in which there is formed an intimate blend of polymer material P1 and polymer material P2, the blend is extruded through a die and the extruded film is stretched after extrusion, in which the flow passage through the die comprises an exit orifice having an exit gap, characterised in that upstream from the exit orifice there is provided a grid chamber comprising one or more grids through which the blend passes, the grid or grids having at least 4 (in the longitudinal sections perpendicular to the main surfaces of the flow) closely spaced lamellae having walls extending several millimeters in the direction of the flow and between the lamellae apertures of a size selected to reduce the average size of the dispersed phase of P1′ or P2′ in the blend, the grid or grids being located at a position in the chamber where the gap is wider than the said exit gap, the grid chamber further comprising a gap reduction portion between the screen and the die exit wherein the gap through which the blend flows is reduced at least part way to the gap of the die exit.